Conventionally, as an underground structure cover, one having an inclined receiving structure is common in which the cover body is fitted in and supported by the receiving frame so that an inclined surface formed at the outer circumference of the cover body is wedged inside an inclined surface formed at the inner circumference of the receiving frame. As an underground structure cover having this inclined receiving structure, Japanese Unexamined Patent Publication No. sho 53-72357 discloses one in which the angle of inclination of the inclined surface with respect to the vertical plane, that is the vertical angle, is limited to 5° to 10°. In the underground structure cover disclosed in Japanese Unexamined Patent Publication No. sho 53-72357, by limiting the vertical angle like this, it is ensured that the cover body is wedged into the receiving frame by a sufficient force by a sufficient depth. By this, the cover body's wobbling, shaking or rattling can be suppressed to a great degree, and the cover body is almost prevented from riding up (becoming inclined instead of staying horizontal).
While the underground structure cover disclosed in Japanese Unexamined Patent Publication No. sho 53-72357 has the above-mentioned beneficial effects, the cover body thereof can be wedged into the receiving frame too deeply, in some setting environment. Thus, sometimes a large amount of labor is required to open the cover with a bar, and sometimes there is difficulty in opening the cover.
Further, in the case such that a load is applied to the cover body in a manner concentrated on a peripheral part thereof, the cover body may be fitted in and supported improperly, which may cause the cover body to become inclined or ride up.
In order to prevent the cover body from being wedged into the receiving frame too deeply, Japanese Examined Utility Model Publication No. sho 60-19162 discloses an underground structure cover in which the inclined surface of the cover body includes an intermediate gently-inclined part and the inclined surface of the receiving frame includes an intermediate gently-inclined part, so that, when the cover body is fitted in the receiving frame with their inclined surfaces meeting each other, a gap is left between the gently-inclined part of the cover body and the gently-inclined part of the receiving frame.
However, in the underground structure cover disclosed in Japanese Examined Utility Model Publication No. sho 60-19162, the gap can only delay the cover body getting wedged deeper (sinking) into the receiving frame, and cannot provide a fundamental solution for preventing the cover body from being wedged in too deeply. Further, no consideration is given to the problem that the cover body becomes inclined or rides up.